(204d) Low Temperature Processing of Bio-Oil for Graphite Production

Iron-catalyzed graphitization of renewable biocarbon is a promising route for graphite synthesis, offering significantly lower temperature processing (~1500 °C) compared to the current commercial synthetic graphite production (>2800 °C). This study reports graphite production from pyrolysis bio-oil using iron as the graphitization catalyst. Efficient mixing of bio-oil and catalyst is a prerequisite for graphite production. However, extensive foaming was observed when iron powder was mixed into the bio-oil due to the presence of organic acids in bio-oil. To address foaming, five different pathways were explored including the use of defoamers, use of iron oxide (Fe₂O₃) as graphitization catalyst, adjusting acidity of bio-oil, high-temperature coking of bio-oil (300-500 °C), and low-temperature pretreatment of bio-oil (100-200 °C). Addition of defoamers failed to prevent foaming, while addition of iron oxide in place of iron resulted in no foaming. However, the quality of graphite produced using iron oxide catalyst was very poor. Adjusting bio-oil pH to 11 was helpful in preventing foaming; however, no attempt was taken to make graphite form the highly alkaline bio-oil. The high-temperature (300-500 °C) coking pathway converted the bio-oil into a highly swelled coke carbon structure when bio-oil was heat treated at 300-500 °C without iron under nitrogen atmosphere. Milling this swelled coke into fine powder was found challenging, which led to poor mixing with iron. This ultimately led to poorly crystalline graphite production, which is inappropriate for lithium-ion battery (LIB) anode applications. A low-temperature pretreatment pathway (150 °C for 5 h) effectively converted the raw bio-oil into a physical powder form well suited for iron mixing and subsequent conversion into LIB-grade graphite anode. This pathway successfully avoided the viscosity, foaming, swelling, and aging issues associated with bio-oil processing. This low-temperature pretreatment pathway could be a milestone in scaling up graphite production from bio-oil.